Wideband highly linear amplifier

ABSTRACT

A wideband highly linear amplifier includes a plurality of pre-distortion units for respectively linearizing digital signals of a plurality of bands, a synthesis unit for synthesizing output signals of the pre-distortion units, a single amplifier for amplifying signals outputted from the synthesis unit, distribution units for respectively separating the signals for each of the plurality of bands from the output signals of the amplifier, a plurality of inverse compensation attenuators for respectively attenuating the separated signals for each of the plurality of bands, and a feedback path for respectively feeding the attenuated signals for each of the plurality of bands back into the pre-distortion unit of the corresponding band out of the plurality of the pre-distortion units.

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation of U.S. application Ser. No. 14/411,479, filed onDec. 26, 2014, which is a National Stage of International ApplicationNo. PCT/KR2013/012042, filed on Dec. 23, 2013, which claims priorityfrom Korean Application No. 10-2013-0121235 filed Oct. 11, 2013, thecontents of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to a wideband highly linear amplifier forcompensating for nonlinear characteristics of a power amplifier in amulti-band system.

BACKGROUND ART

To use linearly a power amplifier, a method of backing off the poweramplifier or utilizing a linearizer is applied. However, the back-offmethod secures the linearity thereof, but has a problem that the outputpower and efficiency are decreased. Further, since the additionallinearizer has a technical limit that it can support a bandwidth just upto a maximum of 100 MHz, the communication equipment such as adistributed antenna system for receiving a plurality of service bandsrequires the power amplifiers as many as the number of the service bandsthereby causing an increase in power consumption, size, price and thelike of communication devices.

DISCLOSURE Technical Problem

The present invention is to provide a wideband highly linear amplifierhaving high efficiency and high linearity characteristics in amulti-band system.

Further, the present invention is to provide a wideband highly linearamplifier which enables a stable output control for each service, i.e.,each band, thereby improving the call quality and maintaining theperformance of an entire system.

Further, the present invention is to provide a single wideband highlylinear amplifier for providing a pre-distortion technique thatcompensates for nonlinear characteristics in a transmitter supportingmulti-band/multi-mode, thereby enabling a passing multi-band signal toeliminate the interference between the multi-band signals according tothe nonlinear characteristics, and enabling each band characteristic tobe shared to have a linear characteristic.

Technical Solution

According to an aspect of the present invention, a wideband highlylinear amplifier includes: a plurality of pre-distortion units forrespectively linearizing digital signals of a plurality of bands; asynthesis unit for synthesizing output signals of the pre-distortionunits; a single amplifier for amplifying signals outputted from thesynthesis unit; distribution units for respectively separating thesignals for each of the plurality of bands from the output signals ofthe amplifier; a plurality of inverse compensation attenuators forrespectively attenuating the separated signals for each of the pluralityof bands; and a feedback path for respectively feeding the attenuatedsignals for each of the plurality of bands back into the pre-distortionunit of the corresponding band out of the plurality of thepre-distortion units.

According to an embodiment, the wideband highly linear amplifier mayfurther include a plurality of attenuators for respectively attenuatingsignals outputted from the pre-distortion units.

According to another embodiment, the sum of control amounts by theinverse compensation attenuator and the attenuator provided in a sameband out of the inverse compensation attenuator and the attenuator maybe uniformly controlled so that a loop gain is maintained.

According to still another embodiment, the sum of the control amount bythe inverse compensation attenuator and the attenuator may be 30 dB.

According to yet another embodiment, the inverse compensation attenuatorand the attenuator may control the output in the range of 0 to 30 dB.

According to still yet another embodiment, the pre-distortion unit maybe a digital pre-distortion unit having a crest factor reduction (CFR)function.

According to further embodiment, the distribution unit may separate thesignals for each of the plurality of bands so that the signals have aband at least twice the size of each band.

According to another further embodiment, the amplifier may be a nitride(GaN) amplifier.

Advantageous Effects

According to the preferred embodiments of the present invention, thepresent invention enables the inverse compensation via the feedback loopthereby performing a stable control of the output for each band,maintaining the performance of the entire system and improving the callquality.

According to the preferred embodiments of the present invention, inprocessing signals of a multi-band, since the single amplifier is used,it enables a reduction in the size thereof and has high efficiency andhighly linear characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a wideband highly linear amplifieraccording to an embodiment of the present invention.

FIG. 2 is a block diagram a feedback loop included in the widebandhighly linear amplifier according to an embodiment of the presentinvention.

BEST MODE FOR THE INVENTION

The present invention may be changed in various forms and embodied indifferent forms, and thus exemplary embodiments of the present inventionwill be described below in more detail with reference to theaccompanying drawings. However, it will be understood that presentdescription is not intended to limit the invention to those exemplaryembodiments. On the contrary, the invention is intended to cover notonly the exemplary embodiments, but also various alternatives,modifications, equivalents and other embodiments, which may be includedwithin the sprit and scope of the invention.

Detailed descriptions of known functions and configurations which havebeen deemed to make the gist of the present invention unnecessarilyobscure will be omitted below. Further, the numbers (e.g., the first,second, etc.) used in the course of being described in the specificationare used just to distinguish one component from the other components.

Further, in this specification, when referred to as one component “isconnected to” or “is accessed to” the other component, it may beunderstood that the one component is connected directly to the othercomponents, but, as long as any particular descriptions to the contraryare not made, it should be understood that the one component may beconnected or accessed to the other component via another component inthe middle thereof.

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings.

The wideband highly linear amplifier according to one embodiment of thepresent invention will be described with reference to FIG. 1. FIG. 1 isa block diagram showing the wideband highly linear amplifier accordingto one embodiment of the present invention.

The wideband highly linear amplifier according to the present embodimentis provided with an amplification path for amplifying signals, and isprovided with a feedback path for feeding back a portion of the outputsignals. As shown in FIG. 1, the path for amplification is provided withpre-distortion units 30, attenuators 40, a synthesis unit 50, and anamplifier 60, and the path for feedback includes distribution units 70and inverse compensation attenuators 80.

Specifically, the wideband highly linear amplifier according to thepresent embodiment may amplify the signals of multi bands. For example,as shown in FIG. 1, three bands of x, y and z, e.g., three types ofservices may be provided.

The signals of each band are mixed with a local oscillation frequency inthe mixer 10 provided for each band thereby being converted into anintermediate frequency signal. The signal having been converted into theintermediate frequency signal is then converted into a digital signalthrough the analog/digital converter 20 provided for each band.

The pre-distortion units 30 are provided in the number corresponding tothe plurality of bands described above, each of which performs thelinearization of the digital signal for each band. In the case ofhigh-power amplifier, it operates in a saturation point, and a nonlineardistortion is thereby generated to cause distortion of signal, thusaffecting an adjacent channel. The pre-distortion unit 30 performs alinearization technique in order to minimize the amplitude distortionand phase distortion of the signal and the influence of the adjacentchannels caused by the nonlinear characteristic of the amplifier.

The pre-distortion unit 30 serves to create an inter-modulationdistortion signal having been reverse-phased and input it to theamplifier. The inputted signal reverse-phased is synthesized with theinter-modulation distortion signal outputted from the amplifier and thenremoved.

On the other hand, the pre-distortion unit 30 according to thisembodiment is provided with a digital pre-distortion (PDP) device with acrest factor reduction (CFR) function. The pre-distortion unit 30 may beadapted even to any environmental changes to maintain itscharacteristics, through the digital pre-distortion device with thecrest factor reduction function received with the inter-modulationdistortion signal through the feedback path.

The attenuator 40 is provided with the number corresponding to theplurality of bands described above, and attenuates the digital signalfor each band outputted from the pre-distortion unit 30.

The synthesis unit 50 synthesizes the signals for each band outputtedthrough the pre-distortion 30 and the attenuator 40 as one signal.

The amplifier 60 amplifies and outputs the signal synthesized as one bythe synthesis unit 50. That is, in the amplifier 60, the signals of x,y, z bands are amplified in the synthesized state and outputted.

There amplifier 60 according to this embodiment may be an amplifierusing a high power nitride transistor (GaN Transistor). In the case ofthe nitride transistor, it is 10 times higher in its power density thanthe existing Si-based LDMOS transistor and has an excellent widebandcharacteristic. By using the GaN Transistor for high power, it ispossible to miniaturize the product and achieve a weight reduction of30% or more.

Incidentally, a portion of the amplified and synthesized signals is, asdescribed previously, fed back to the pre-distortion unit 30 through thedistribution unit 70 and the inverse compensation attenuator 80.

In the case where the feedback path is not provided, the characteristicchange of the amplifier may occur severely at a time of temperaturechange and control of changing input level and output level.

The wideband highly linear amplifier according to the present embodimentperforms an inverse compensation through the feedback loop structuredescribed above thereby having an effect of maintaining thecharacteristics of the amplifier so that the characteristics may not bechanged as far as possible even when the environment is changed or acontrol of changing input and output levels is performed.

More specifically, the distribution unit 70 separates again the signalsfor each of the plurality of bands from the output signals of theamplifier 60. The distribution unit 70 may redistribute for each bandthe signals outputted through the amplifier 60 by performing filteringusing a filter or the like corresponding to each band after separatingthe signals.

Further, it is possible for the distribution unit 70 to separate thesignals to have a band approximately twice the size of each band whenseparating the signals for each of the plurality of bands. If thesignals are separated so as to have the band approximately twice thesize of each band, it is effective to improve the performance reductiondue to a third harmonic current (IM).

The signals separated for each band are inputted to each of the inversecompensation attenuator 80 provided by the number of bands. The inversecompensation attenuator 80 attenuates the signals for each band outputfrom the distribution unit 70.

At this time, it is preferable that the inverse compensation attenuator80 control the output signals in the range of less than 30 dB, and it ispreferable to maintain uniformly the sum of the control amount of theinverse compensation attenuator 80 and the control amount of theattenuator 80 described previously. By maintaining uniformly the sum ofthe control amount of the inverse compensation attenuator 80 and thecontrol amount of the attenuator 80 described previously, it is possibleto maintain the loop gain returned to the pre-distortion unit 30 by wayof the amplifier 60.

As such, in the case where the inverse compensation attenuator 80 is notprovided for each band, it is not able to adjust the output of theamplifier 60 for each band. In addition, even though the attenuator foreach band is applied to the front end of the pre-distortion unit 30, thedigital pre-distortion unit deteriorates in the signal to noise ratio(S/N) thereby having a big effect on the call quality at the time anattenuation of 10 dB or more occurs, because of the technicallimitations of dynamic range of the analog/digital converter.

As such, since the attenuator 40 is provided at the front end of theamplifier 60 and the inverse compensation attenuator 80 is provided tothe feedback path thereby enabling the inter-inverse compensation, it ispossible to stably adjust the output of the amplifier 60 for each bandby maintaining the loop gain and it is possible to adjust the output ofthe amplifier 60 for each band by 30 dB or more.

Further, in addition to the feedback structure including the attenuator40 enabling the inter-inverse compensation and the inverse compensationattenuator 80, since the digital pre-distortion device (DPD) having thecrest factor reduction (CFR) function is provided, it is possible topositively adapt to any environmental changes thereby maintaining thecharacteristics of the wideband highly linear amplifier.

The characteristics of the wideband highly linear amplifier according toan embodiment of the present invention will be described with referenceto FIGS. 1 and 2. FIG. 2 is a block diagram showing the feedback loopincluded in the wideband highly linear amplifier according to anembodiment of the present invention.

The signals for each of the plurality of services with different bandsare linearization-compensated through the pre-distortion unit 30,respectively, and then combined into one signal to be amplified as arequired output through the single of amplifier 60.

The signal which is amplified and output from the amplifier 60 is againseparated into the signal for each band through the distribution unit 70on the feedback path and then transferred again to the pre-distortionunit 30 via the inverse compensation attenuator 80. Due to suchstructure, in spite of external environmental changes or changes causedby input and output control, it is possible to maintain the linearitythereof. In addition, it is possible to control the output for each bandof each service through the inter-inverse compensation attenuatingprocess of the attenuator 40 and the inverse compensation attenuator 80.

Meanwhile, as described above, it is preferable to uniformly maintainthe sum of the control amount of the inverse compensation attenuator 80and the control amount of the attenuator 40. Table 1 below indicates theinter-inverse compensation attenuating operation.

TABLE 1 Inverse compensation Attenuator attenuator Sum 0 30 30 1 29 30 228 30 ~ ~ ~ 30 0 30

The attenuator 30 and the inverse compensation attenuator 80 may becontrolled in the range of 0 to 30 dB. In the case where the controlamount of the attenuator 30 is 1 dB, the control amount of the inversecompensation attenuator 80 is controlled as 29 dB so that the sum of thecontrol amount of the inverse compensation attenuator 80 and the controlamount of the attenuator 40 becomes 30 dB.

Referring to FIG. 2, the pre-distortion unit 30, the route connectingthe attenuator 40, the amplifier 60 and the inverse compensationattenuator 80 forms a single loop. At this time, since the sum of thecontrol amount of the inverse compensation attenuator 80 and the controlamount of the attenuator 40 as described previously is maintaineduniformly, the loop gain returning to the pre-distortion unit 30 via theamplifier 60 may be uniformly maintained.

When the gain of the route from the pre-distortion unit to the feedbackpath is changed through an external environment and a control,difference in the exact inverse compensation for the AM-AMcharacteristic of the amplifier is generated thereby causing theperformance degradation. Accordingly, if the output control is performedfor each service without the inter-inverse compensation attenuatingprocess, it may affect the call quality.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

The invention claimed is:
 1. An amplification system, comprising: aplurality of first attenuators, each of the first attenuatorsattenuating a corresponding one of linearized signals of a plurality ofbands; a combining unit for combining output signals of the firstattenuators; an amplifier for amplifying an output signal of thecombining unit; a separation unit for separating an output signal of theamplifier for each of the plurality of bands; and a plurality of secondattenuators, each of the second attenuators attenuating a correspondingone of the separated signals for each of the plurality of bands.
 2. Theamplification system of claim 1, further comprising: a linearizer forlinearizing signals of the plurality of bands.
 3. The amplificationsystem of claim 2, wherein the linearizer is a digital pre-distorterhaving a crest factor reduction (CFR) function.
 4. The amplificationsystem of claim 2, further comprising: a feedback path for feeding eachof output signals of the plurality of second attenuators back into thelinearizer.
 5. The amplification system of claim 1, wherein a sum ofcontrol amounts of a first attenuator and a second attenuator providedin a same band among the first attenuators and the second attenuators isuniformly controlled so that a loop gain is maintained.
 6. Theamplification system of claim 5, wherein the sum of the control amountsof the first attenuator and the second attenuator is about 30 dB.
 7. Theamplification system of claim 6, wherein the first attenuator and thesecond attenuator control an output in a range of about 0 to about 30dB.
 8. The amplification system of claim 1, wherein the separation unitseparates the output signal of the amplifier for each of the pluralityof bands so that the separated signals have a band at least twice a sizeof each band.
 9. The amplification system of claim 1, wherein theamplifier is a gallium nitride (GaN) amplifier.
 10. An amplificationsystem, comprising: a first attenuation unit for attenuating linearizedsignals of a plurality of bands; a combining unit for combining outputsignals of the first attenuation unit; an amplifier for amplifying anoutput signal of the combining unit; and a second attenuation unit forattenuating an output signal of the amplifier, wherein a sum of controlamounts of the first attenuation unit and the second attenuation unit isuniformly controlled so that a loop gain is maintained.
 11. Theamplification system of claim 10, further comprising: a linearizer forlinearizing signals of the plurality of bands.
 12. The amplificationsystem of claim 11, further comprising: a feedback path for feeding anoutput signal of the second attenuation unit back into the linearizer.13. The amplification system of claim 10, wherein the sum of the controlamounts of the first attenuation unit and the second attenuation unit isabout 30 dB.
 14. The amplification system of claim 13, wherein the firstattenuation unit and the second attenuation unit control an output in arange of about 0 to about 30 dB.